CWG-68: Ensure dependencies are installed as part of package

{{cookiecutter.project_slug}}/pyproject.toml

 [build-system]
 requires = [
-    "setuptools>=45",
+    "setuptools>=62.6",
     "setuptools_scm[toml]>=6.2",
     "wheel"
 ]

{{cookiecutter.project_slug}}/requirements.txt

-numpy >= 1.20.0 # BSD
+importlib-metadata>=0.12, <5.0;python_version<"3.8"
+numpy

{{cookiecutter.project_slug}}/setup.cfg

@@ -29,9 +29,7 @@ classifiers =
 include_package_data = true
 packages = find:
 python_requires = >=3.7
-install_requires =
-    importlib-metadata>=0.12, <5.0;python_version<"3.8"
-    numpy
+install_requires = file: requirements.txt
 
 [flake8]
 max-line-length = 88